Is powerfull Amps only for low sensitivity speakes?

I’ve heard it said many times that you cannot have too much power, but under-powering speakers and causing the high transients to clip the signal can do damage to any speaker; therefore, it is good to have headroom for the speakers in which to have room to function and breath properly. Using a water analogy . . . the fire department wouldn’t use a garden hose to put out a large fire. Even if there was plenty of water pressure, the hose could not handle it and would probably burst, and even if the hose was strong enough to handle that water pressure (power), it would not have the diameter to produce the VOLUME of water necessary to do the job.  Having all that water pressure . . . the firemen are always prepared in any given situation to do the job; however, if the water source does not have the pressure -- no matter the associated equipment and controls, the firemen can open up their hoses at full throttle . . . and they will only get so much volume coming out, and the building will burn.  Simply put, the right tools/sources to do the right job will produce the desired results and without disappointment -- if used with the proper knowledge, skills, and wisdom.

In the case of the power amp(s) being expensive, there are some class D amplifiers, that have capabilities of taking on various efficient to inefficient speakers like from 2 ohms up to 8 ohms or more with no sweat. In fact, some do so with great sound and not a high end price . . . i.e. a Crown XLS 1502 is rated at: watts/side @ 8 ohms: 330W; watts/side @4 ohms: 525W; and at watt/side @ 2 ohms: 775W. So you see, there is plenty of headroom, and this amp has level limiters so that you can set the highest limit of the amplifier’s volume to match the volume control of your preamp or input device so that you will not blow out your speakers or your ears. They have one model that has less power . . . and two models with higher power, I believe, in the XLS model.

In any case, it is always nice to have options and at reasonable prices. I have relatively inefficient speakers running at approximately 8 ohms and rated for up to 200 watts of power, and this amplifier, which can also be bridged into even higher power, has absolutely no problem running these speakers. In fact, I use a DBX to control my sound system to tune it to the room and have control over the way the speakers sound, and have thought about turning my speakers into active speakers with the DBX acting as an electronic crossover and using Crown amps for each frequency band. Right now I have the Crown operating the main speakers and my old monoblocks B&Ks (250 watts each) running the subwoofers, and the blend is seemless as the levels between the two. can easily be controlled. It is always nice to have options and versatility . . . and the Crowns do give you exactly those options.

My experience is that inefficient speakers just never quite sound right to me, regardless of how much power the amp supposedly has. They always sound somewhat sluggish, effortful, leached-out, and, my horror-words in the audiophilic realm: "neutral" (means: bland) and "transparent" (means: thin). 87dB is the lower limit for me, 89dB is better, over 90dB is better. Then I'm free to use tube amps, EL34s, single-ended Alephs, sweet Creeks, integrateds, whatever I want. To low-sensitivity speakers I say "bah, humbug." I've yet to meet a high-wattage amp that honestly sounds really good, and I used to work in a high-end audio salon so I've heard amps that cost up to $25,000/pair. In my mind they just get you back to where you would have been in the first place if you'd gone with speakers of decent efficiency. Just my personal opinion according to the ears attached to my own head, YMMV.

It should be no surprise that 15" drivers, regardless of their so called efficiency (or sensitivity), need higher voltages (or power) to operate at their best. You still need to move that large amount of air and that takes juice. In my opinion (hopefully a fact), the reason why a tube amplifier may sound a bit more "muddy" in the low octaves when compared to an SS amplifier is not (necessarily) due to the power rating, its mostly because of the typically much lower damping factor of the tube design. That usually translates to a "looser" bass. You'd have the same result even when you compare the amps - tube vs. SS, with identical power rating. The OTLs are exceptions because they tend to have an un-tube like very low output impedance thus a higher than average damping factor.

The answer is No for low sensitivity and don't be confuse with the motion that tube amps work only with 87 or 92 db range.  What you need is high efficiency speakers that will work properly in every amp category.

Some speakers require amplifiers with a higher damping factor (DF) and some speakers sound their best with lower DF amplifiers. The desirable level of DF is determined by the speaker design and the intentions of the speaker builder.

You can increase DF and inversely lower amplifier output impedance by utilizing more NFB. Some amplifiers tout DF level of 1000 or even higher. This ultra level of DF doen’t correlate with better sound quality.

There are speakers that sound superb driven by amplifiers with a DF of 2 or 3. It all depends on the speaker design mandate.
Charles

Pairing of speakers with amp is really the key to any system. It's not just efficiency and power, it's clarity at desired volumes, voicing, damping, etc. I've always been of the opinion that you choose, in order: room, desired listening volumes, then speakers, then try different amps until you understand what the different amps are doing, then choose your amp. Bass in-room is the downfall of many an a'phile, most of whom cannot recognize standing waves when they hear the effect. Many audiophiles cannot hear when speakers are wired out of phase!

Kalali 1-20-2018
The OTLs are exceptions because they tend to have an un-tube like very low output impedance thus a higher than average damping factor.

Hi Kalali,

This is a rare instance in which I must correct an oversight in your usually sage commentary. OTL power amps do NOT have very low output impedance. A fundamental purpose of the output transformers that are incorporated into most tube amp designs is to transform the typically very high impedance of tube-based circuits to a much lower output impedance, which is accomplished by stepping down the signal voltage provided by those tubes while stepping up the current. OTLs typically compensate for the lack of the impedance conversion a transformer would provide by using a plurality of output tubes, and by choosing tubes suited to operation at relatively low voltages, but nevertheless the resulting output impedances and damping factors are usually in the same ballpark as those of many tube amps which have output transformers.

Atma-Sphere OTLs, for example, have damping factors ranging from a bit more than 1 to around 5 or so. An OTL that used to be made by Tenor had a higher damping factor, around 20, but even so the recommended load impedance for that amp was 8 ohms minimum.

Also, speaking of sage commentary, +1 to everything in the post by Charles which followed shortly after yours.

Best regards,
-- Al

Interesting discussion.  I think at a certain point it just becomes about taste and experience.  Also what are our sources?  I'm a klipsch man myself, and am only interested in a pure analog system; mostly acoustic vinyl, tube pre, low watt tube amps, super high sensitivity horn speakers (Chorus).  I recently upgraded from 150 watt hybrid amp (moscode 300) to 20 watt monoblocks (quicksilver horn monoblocks).  I loved the moscode but there was always a little background hum, the lower watt amps are dead silent, and, in my very subjective opinion, show slightly more detail.  But my system certainly doesn't go as loud as it did, I tradeoff I can live with.  I've heard quad electrostatic speakers that are power hungry and sound incredible, but I decided not to pursue as I'd have to rebuild my whole system around them.  There is also the question of how much electricity you want to be burning.  To me the elegance of big, highly efficient speakers with super low watt amplification is very attractive (I'd love to try a really low watt single ended amp on my Klipsch), but I'm sure the right combination of small, inefficient speakers with mammoth solid state amp can also produce great sound.  In the end it's a matter of aesthetics, musical preferences, and $$.  

This may be interesting: http://www.harbeth.co.uk/usergroup/forum/the-science-of-audio/amplifier-matching-mismatching-and-cli...
The point is that with significant dynamic range the peak power required is much higher than the average. In the quoted example, if you need 1 watt on average, you will need 160 watt to cope with a 22 dB peak above that average.

So I guess you started the equation with a lower power requirement for average level, by e.g. using more efficient speakers and/or a small listening room. And 4 Ohm is also pretty low.

+1 - Agree with Trelja and Noromance

From my 35+ years experience in this hobby, power corrupts, and have your ever really heard how loud 1 watt/channel can get?  We only have 1 set of ears and I like mine to last as long as possible.  A lesson I was taught many years ago by a stereo shop owner who was tone deaf but built the most amazing sounding speakers.

 I have heard great sounding systems with both very efficient speakers and not so efficient speakers. But I do feel that with dynamic drivers if you go below around 90 DB you cannot get the really really great sound.  No matter how much power you add you cannot get the macro dynamics.   
 I believe the industry moved more towards less efficient speakers because they are much cheaper to manufacture as you don't need the tight tolerances.   And with the transistor it was easier to get big power so efficiency was not quite as important, or so they thought. 

Are powerful amps only for low sensitivity speakers? No.

My 4-way hybrid-horn/dipole system is powered by eight identical Class D amplifiers. Each amp is rated 175W RMS, 325W peak power into 8 Ohms.

The compression driver mid horns and tweeters are very sensitive, about 110 dB/W/meter.

The four 15" woofers in four U-frames are each about 95 dB/W/M.

I don't know the overall system sensitivity - the horns had to be padded down by the active crossover to match the woofers - but it's pretty high. Total power is 1,400 W RMS/ 2,600 W, peak power.

I never push SPLs very high, I want to preserve what's left of my hearing, so usually power is under 1 watt, with brief peaks of 10, or 15 watts, maybe. Lots of head room. Sounds very good.

My 1.5 W/channel Type 45 SET amp, on the other hand, also sounds very good powering sensitive horns. And that little amp has pretty much no headroom.

It's just a hunch but I would be surprised if 60W RMS pumped into 100db sensitivity sepakers doesn't at some point on bass heavy material run toward clipping. This is pretty much what I run and given my fondness of dynamic range and dislike of amp clipping I really wouldn't go below 60W.
For the more technically minded members here, given a 22' by 16.5' with 8'9" ceiling, well trapped room does 60 watts ever clip? I play it pretty loud but do the peaks require the full amp?

Dear Friends, thank you again for your comments.
May I ask your comments also for the difference between single ended triode amps and push pull tube amps in terms of 2nd and 3rd harmonics capabilities.
regards,
ozan

Power is relative.  My wife has a Mini Audio system. Cheap,Cheap!  For what it is a $300.00 complete 10 CD changer, Radio, and 6" small bookshelf speakers.  It is rated at 100W RMS/ channel. the unit will get very loud, however it has no balls.  I have a 50W RMS / channel Crown PL-1 (22,000mf reserve capacitance) and in comparison at the same volume level the difference in the dynamics is astounding.  Playing on speakers of 89db /w 1W efficiency and driving about 20W the punch and low end off of the Crown amp is like night and day compared to a double the power rated amp in the cheap system.  It is like comparing a 50W crown to a 50W Mark Levenson amp.  Even though both are rated the same wattage the Levenson power supply would have I am guessing triple reserve in the power supply.  Not to mention the quality of the components from front to end.  So we can talk about watts but that also does not tell how it sounds. Generally you get what you pay for but I always recommend listening side by side on the same equipment.  The lesser wattage amp might sound better depending on what you like.  That is what matters - what you like. 

Someone wrote:
"These statements are not accurate. If the amp makes too much power and the speaker has no need for it, the amp will be operating in a lower power region. With most higher power amps, this means it will have increased distortion. You can see this in their specs. The increased distortion is audible as brightness in most cases and will result in less detail as the distortion will mask lower level signals."

Not True! I wont even start here. I will ask you to think about percentages and hwo the FTC requires amps to be measured.

Power is so so overrated. I have Magnepan 20.7, 86db and I’m currently driving them with a 90wpc tube amp without a problem and to be totally honest they have never sounded better. I use to drive them with ARC DS450M mono-blocks that put out a whopping 450wpc and 600wpc in a 4 ohm load. And to be frank they sounded like crap. I have never listened to music as long as I do with my current setup. Buy a well built amp that has bandwidth and high current and pay less attention with wattage. Just my humble opinion. Let your ears be your guide and not hyperbole. 

May I ask your comments also for the difference between single ended triode amps and push pull tube amps in terms of 2nd and 3rd harmonics capabilities.

Its not as simple as that might sound! SETs tend to make more of the 2nd harmonic than any other, with each successive harmonic at a much lower level than the one preceding it. The 2nd harmonic is where the 'richness' of single-ended operation comes from.

If an amplifier is push-pull, the harmonic structure varies depending on how the push-pull is accomplished. For example, if a single-ended input is employed, the 2nd will be canceled in the load, but there will be some present on account of the input, and you will also see a 3rd and a fairly prominent 5th. Many people that prefer SETs often point to the distortion of traditional push-pull tube amps as most are built this way, as being why SETs sound better.

But that is not the full story.

If the push-pull amp is entirely differential and balanced from input to output, the 3rd harmonic will be the primary distortion component but at levels about the same as the 3rd is seen in an SET. So this is considerably lower distortion and such an amp will tend to sound less romantic and more neutral, but will retain much of the musical character of an SET.

So topology plays a pretty big role and you really have to know what that is about. The 2nd, 3rd and 4th (the lower ordered harmonics) are musical to the human ear. The 5th and above tend to contribute to brightness and harshness, for example we've known since the 1930s that the 7th contributes to a metallic quality. Our ears are particularly sensitive to the higher orders and use them to sense sound pressure. All forms of distortion are perceived as some form of tonality.

"These statements are not accurate. If the amp makes too much power and the speaker has no need for it, the amp will be operating in a lower power region. With most higher power amps, this means it will have increased distortion. You can see this in their specs. The increased distortion is audible as brightness in most cases and will result in less detail as the distortion will mask lower level signals."

Not True! I wont even start here. I will ask you to think about percentages and hwo the FTC requires amps to be measured.

Actually the statement was quite true and simply looking at the distortion specs of the amp in question will bear this out. The FTC really doesn't have much to say about it. They are more concerned with distortion at full output.